My trusty electric fly-zapper broke, so I opened it up to have a look in case it was something simple. I have to say I was a little surprised by what I found inside: the capacitor reads 473K, meaning the capacitance is 47nF (I was able to confirm this with my multimeter).

As the charged voltage of the fly-zapper is about 2.5kV, that gives a total charge of around 120uC. I'm surprised this is so high - as electrical regulations usually say anything above 45uC can be dangerous (see, for instance, IEC 61010-1).

My question is: how is it possible this got through the regulations? Surely as it's almost 3-times the safe charge for a capacitive discharge it should be considered dangerous?

PS: this particular fly-zapper (The Executioner) doesn't have a protective 3-layer grill like some: it's pretty easy to touch the live terminals and it just feels like a static shock.

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    \$\begingroup\$ It's meant to be dangerous ... for the fly! As far as human safety, I imagine that the arrangement of the electrodes makes it difficult, if not impossible, to deliver the entire charge effectively to a human body. \$\endgroup\$
    – Dave Tweed
    Apr 20, 2017 at 22:59
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    \$\begingroup\$ In many countries there are a lot of dodgy products for sale, but there may also be language in certain safety regulations which distinguishes products' designed purpose from happenstance traits. Most devices, for example, shouldn't have any exposed surfaces that exceed 70C, but a soldering iron would be pretty useless if no surface could exceed that temperature. As Dave Tweed noted, the purpose of the zapper is to deliver a fatal charge to a fly, and reducing the charge would likely reduce its effectiveness. \$\endgroup\$
    – supercat
    Apr 20, 2017 at 23:09
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    \$\begingroup\$ Also, it may be taken into consideration that there is virtually no way for this charge to be discharged through a large enough portion of the human body to "zap" anything terribly vital. While the energy may be fairly high, the close proximity of the electrodes will cause it to be carried almost exclusively through the skin. I'm fairly certain you'd have a very difficult time stimulating an involuntary muscle contraction with 2 electrodes only 2-3mm apart, and basically impossible to have any meaningful portion of the current reach cardiac tissue(s). \$\endgroup\$ Apr 20, 2017 at 23:20
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    \$\begingroup\$ It's called the executioner so doesn't this mean anything to you. Is it CE marked. If so request a technical file to see the legal justification for the CE mark. \$\endgroup\$
    – Andy aka
    Apr 21, 2017 at 0:24
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    \$\begingroup\$ @KurtNewman The manufacturer will have produced and filed a Document of Conformity (DoC) for the product. In the UK (and I assume elsewhere) consumers can't access these documents directly. They have to go through public authorities designated as "Market Surveillance Authorities". In the UK, MSAs include bodies like the Trading Standards Institute, the Health and Safety Executive, the Vehicle Certification Agency, etc. The UK Citizens Advice Bureau has a helpline which will assess your complaint and advice how to pass it to Trading Standards if appropriate. \$\endgroup\$
    – alephzero
    Apr 22, 2017 at 11:58

1 Answer 1


I don't know if this file zapper meets any standard, or how it does it. But it's extremely unlikely that the 4.7nF cap is 4.7nF at 2.5KV, particularly if 4.7nF is what you measured with your multimeter.

If you told me that the effective capacitance as 2.8nF I wouldn't be surprised. If you suggest that the working capacitance is 1n5F, I'd just say that I don't have the specifications for that capacitor.


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